English originally used a four-form system up to and including Early Middle English but Modern English has reduced this to a two-form system consisting of just 'yes' and 'no'. Some languages do not answer yes–no questions with single words meaning 'yes' or 'no'. Welsh and Finnish are among several languages that typically employ echo answers (repeating the verb with either an affirmative or negative form) rather than using words for 'yes' and 'no', though both languages do also have words broadly similar to 'yes' and 'no'. Other languages have systems named two-form, three-form, and four-form systems, depending on how many words for yes and no they employ. Some languages, such as Latin, have no yes-no word systems.

The words yes and no are not easily classified into any of the eight conventional parts of speech. Although sometimes classified as interjections, they do not qualify as such, and they are not adverbs. They are sometimes classified as a part of speech in their own right, sentence words, word sentences, or pro-sentences, although that category contains more than yes and no and not all linguists include them in their lists of sentence words. Sentences consisting solely of one of these two words are classified as minor sentences.

The differences among languages, the fact that in different languages the various words for yes and no have different parts of speech and different usages, and that some languages lack a 'yes-no' word system, makes idiomatic translation difficult.

Although sometimes classified as interjections, these words do not express emotion[dubious– discuss] or act as calls for attention; they are not adverbs because they do not qualify any verb, adjective, or adverb. They are sometimes classified as a part of speech in their own right, sentence words or word sentences.[1][2][3]

Georg von der Gabelentz, Henry Sweet, and Wegener have all written on the subject of sentence words, Wegener calling them "Wortsätze". Both Sweet and Wegener include yes and no in this category, with Sweet treating them separately from both imperatives and interjections, although Gabelentz does not.[5]

Watts[6] classifies yes and no as grammatical particles, in particular response particles. He also notes their relationship to the interjections oh and ah, which is that the interjections can precede yes and no but not follow them. Oh as an interjection expresses surprise, but in the combined forms oh yes and oh no merely acts as an intensifier; but ah in the combined forms ah yes and ah no retains its standalone meaning, of focusing upon the previous speaker's or writer's last statement. The forms *yes oh, *yes ah, *no oh, and *no ah are grammatically ill-formed. Aijmer[7] similarly categorizes the yes and no as response signals or reaction signals.

Ameka classifies these two words in different ways according to context. When used as back-channel items, he classifies them as interjections; but when they are used as the responses to a yes-no question, he classifies them as formulaic words. The distinction between an interjection and a formula is, in Ameka's view, that the former does not have an addressee (although it may be directed at a person), whereas the latter does. The yes or no in response to the question is addressed at the interrogator, whereas yes or no used as a back-channel item is a feedback usage, an utterance that is said to oneself. However, Sorjonen criticizes this analysis as lacking empirical work on the other usages of these words, in addition to interjections and feedback uses.[8]

Bloomfield and Hockett classify the words, when used to answer yes-no questions, as special completive interjections. They classify sentences comprising solely one of either of these two words as minor sentences.[2]

Sweet classifies the words in several ways. They are sentence-modifying adverbs, adverbs that act as modifiers to an entire sentence. They are also sentence words, when standing alone. They may, as question responses, also be absolute forms that correspond to what would otherwise be the not in a negated echo response. For example, a "No." in response to the question "Is he here?" is equivalent to the echo response "He is not here." Sweet observes that there is no correspondence with a simple yes in the latter situation, although the sentence-word "Certainly." provides an absolute form of an emphatic echo response "He is certainly here." (Many other adverbs can also be used as sentence words in this way.)[9]

Unlike yes, no can also be an adverb of degree, applying to adjectives solely in the comparative (e.g. no greater, no sooner, but not no soon or no soonest), and an adjective when applied to nouns (e.g. "He is no fool." and Dyer's "No clouds, no vapours intervene.")[9][10]

Grammarians of other languages have created further, similar, special classifications for these types of words. Tesnière classifies the French oui and non as phrasillons logiques (along with voici). Fonagy observes that such a classification may be partly justified for the former two, but suggests that pragmatic holophrases is more appropriate.[11]

While Modern English has a two-form system of yes and no for affirmatives and negatives, earlier forms of English had a four-form system, comprising the words yea, nay, yes, and no. In essence, yes and no were the responses to a question posed in the negative, whereas yea and nay were the responses to positively framed questions.

Benedick's yea is the answer to a positively framed question. The answers to positively framed questions ("Will he go?") were yea and nay, while the answers to negatively framed questions ("Will he not go?") were yes and no. This subtle grammatical feature of Early Modern English is recorded by Sir Thomas More in his critique of William Tyndale's translation of the New Testament into Early Modern English, which was then quoted as an authority by later scholars:[12]

I would not here note by the way that Tyndale here translateth no for nay, for it is but a trifle and mistaking of the Englishe worde : saving that ye shoulde see that he whych in two so plain Englishe wordes, and so common as in naye and no can not tell when he should take the one and when the tother, is not for translating into Englishe a man very mete. For the use of these two wordes in aunswering a question is this. No aunswereth the question framed by the affirmative. As for ensample if a manne should aske Tindall himselfe: ys an heretike meete to translate Holy Scripture into Englishe ? Lo to thys question if he will aunswere trew Englishe, he must aunswere nay and not no. But and if the question be asked hym thus lo: is not an heretike mete to translate Holy Scripture into Englishe ? To this question if he will aunswere trewe Englishe, he must aunswere no and not nay. And a lyke difference is there betwene these two adverbs ye and yes. For if the question bee framed unto Tindall by the affirmative in thys fashion. If an heretique falsely translate the New Testament into Englishe, to make his false heresyes seem the word of Godde, be his bokes worthy to be burned ? To this questyon asked in thys wyse, yf he will aunswere true Englishe, he must aunswere ye and not yes. But now if the question be asked him thus lo; by the negative. If an heretike falsely translate the Newe Testament into Englishe to make his false heresyee seme the word of God, be not hys bokes well worthy to be burned ? To thys question in thys fashion framed if he will aunswere trewe Englishe he may not aunswere ye but he must answere yes, and say yes marry be they, bothe the translation and the translatour, and al that wyll hold wyth them.

In fact, More's exemplification of the rule actually contradicts his statement of what the rule is. This went unnoticed by scholars such as Horne Tooke, Robert Gordon Latham, and Trench, and was first pointed out by George Perkins Marsh in his Century Dictionary, where he corrects More's incorrect statement of the first rule, "No aunswereth the question framed by the affirmative.", to read nay. That even More got the rule wrong, even while himself dressing-down Tyndale for getting it wrong, is seen by scholars such as Furness as evidence that the distinction between these four words was "truth, too subtle a distinction for practice". Benedick's answer of yea is a correct application of the rule, but as observed by W. A. Wright "Shakespeare does not always observe this rule, and even in the earliest times the usage appears not to have been consistent." Furness notes that this is indeed the case in the following, where Hermia's answer should, in following the rule, have been yes:[12][15]

Demetrius: Do not you thinke, The Duke was heere, and bid vs follow him?Hermia: Yea, and my Father.

Marsh himself found no evidence of a four-form system in Mœso-Gothic, although he reported finding "traces" in Old English. He observed that in the Anglo-Saxon Gospels, positively phrased questions are answered positively with gea (John 21:15,16) and negatively with ne (Luke 12:51; 13:5), nese (John 21:5; Matthew 13:29), and nic (John 18:17); while negatively phrased questions are answered positively with gyse (Matthew 17:25) and negatively with nâ (John 8:10).[15]

Marsh calls this four-form system of Early Modern English a "needless subtlety". Tooke called it a "ridiculous distinction", with Marsh concluding that Tooke believed Thomas More to have simply made this rule up and observing that Tooke is not alone in his disbelief of More. Marsh, however, points out (having himself analyzed the works of John Wycliffe, Geoffrey Chaucer, John Gower, John Skelton, and Robert of Gloucester, and Piers Ploughman and Le Morte d'Arthur to see where and how these words were used) that the distinction both existed and was generally and fairly uniformly observed in Early Modern English from the time of Chaucer to the time of Tyndale. "Yes" and "no" were reserved for answering negatively phrased questions, and yea and nay served both as answers to positively phrased questions and as normal intensifiers in responses to noninterrogative statements. But after the time of Tyndale, the four-form system was rapidly replaced by the modern two-form system.[15]

Several languages have a three-form system, with two affirmative words and one negative. In a three-form system, the affirmative response to a positively phrased question is the unmarked affirmative, the affirmative response to a negatively phrased question is the marked affirmative, and the negative response to both forms of question is the (single) negative. For example, in Norwegian the affirmative answer to "Snakker du norsk?" ("Do you speak Norwegian?") is "Ja", and the affirmative answer to "Snakker du ikke norsk?" ("Do you not speak Norwegian?") is "Jo", while the negative answer to both questions is "Nei".[15][16][17][18][19]

Swedish, and to some extent Danish and Norwegian, also has additional forms javisst and jovisst, analogous to ja and jo, to indicate a strong affirmative response. Swedish (and Danish slang) also have the forms joho and nehej, which both indicate stronger response than jo or nej. Jo can also be used as an emphatic contradiction of a negative statement.[17][20]

Like Early Modern English, the Romanian language has a four-form system. The affirmative and negative responses to positively phrased questions are da and nu, respectively. But in responses to negatively phrased questions they are prefixed with ba (i.e. ba da and ba nu). nu is also used as a negation adverb, infixed between subject and verb. Thus, for examples, the affirmative response to the negatively phrased question "N-ai plătit?" ("Didn't you pay?") is "Ba da." ("Yes."—i.e. "I did pay."), and the negative response to a positively phrased question beginning "Se poate să ...?" ("Is it possible to ...?") is "Nu, nu se poate." ("No, it is not possible."—note the use of nu for both no and negation of the verb.)[21][22][23]

Bloomfield and Hockett observe that not all languages have special completive interjections. In Polish, for example, tak (thus, so) and nie (not) are adverbs. Russian has the adverbs[citation needed]да and нет, and Finnish does not generally answer yes-no questions with either adverbs or interjections but answers them with a repetition of the verb in the question, negating it if the answer is the negative. (This is an echo response.) The answer to "Tuletteko kaupungista?" ("Are you coming from town?") is the verb form itself, "Tulemme." ("We are coming.")

Negative questions are answered similarly. Negative answers are just the negated verb form. The answer to "Tunnetteko herra Lehdon?" ("Do you know Mr Lehto?") is "En tunne" ("I don't know.") or simply "En." ("I don't.").[2][24][25][26] However, Finnish also has particle words for "yes": "Kyllä" (formal) and "joo" (very colloquial). A yes-no question can be answered "yes" with either "kyllä" or "joo", which are not conjugated according to the person and plurality of the verb. "Ei", however, is always conjugated and means "no".

It is often said falsely that Welsh has no words at all for yes and no. It has ie and nage. However, these are used only in specialized circumstances and are but some of the many ways in Welsh of saying yes or no. As in Finnish, the main way to state yes or no, in answer to yes-no questions, is to echo the verb of the question. So the answers to "Ydy Ffred yn dod?" ("Is Ffred coming?") are either "Ydy." ("He is (coming).") or "Nac ydy." ("He is not (coming)."). In general, the negative answer is the positive answer combined with nag. As in Finnish, this avoids the issue of what an unadorned yes means in response to a negative question. While a yes response to the question "You don't like strawberries?" is ambiguous in English, the Welsh response ydw has no ambiguity. The same would apply for Finnish, where the question would be answered with en (I don't). For more information on yes and no answers to yes-no questions in Welsh, see Jones, listed in further reading.[26][27][28]

Irish and other Gaelic languages do not have any words for "yes" or "no". Instead, an echo response of the verb used to ask the question is used. Sometimes, the verb used is "Tá" (to be). Example "An bhfuil sé ag teacht" (Is he coming). Answer: "Tá" (Is) or "Níl" (Is not). More frequently, another verb will be used. Example "Ar chuala sé" (Did he hear). Answer "Chuala" (heard) or "Níor chuala" (Did not hear). Irish people frequently give echo answers in English as well. Example: "Did you hear?" Answer "I heard/I did". This also happens in the Galician language.

Latin has no single words for yes and no. Their functions as intensifiers and interjections are taken up by using the vocative case. Their functions as word sentence responses to yes-no questions are taken up by sentence adverbs, single adverbs that are sentence modifiers and also used as word sentences. There are several such adverbs classed as truth-value adverbs—including certe, fortasse, nimirum, plane, vero, etiam, sane, minime, and videlicet. They express the speaker's/writer's feelings about the truth value of a proposition. They, in conjunction with the negator non, are used as responses to yes-no questions.[2][29][30][31][32] For example:

The Chinese languages use echo responses as well.[34] In all languages, yes-no questions are often posed in A-not-A form, and the replies to such questions are echo answers that echo either A or not A.[35][36] In Mandarin Chinese, the closest equivalents to yes and no are to state "是" (shì; lit. "is") and "不是" (búshì; lit. "not is").[37][38] (In Cantonese Chinese, the preceding are 係 hai6 and 唔係 m4 hai6, respectively.) The phrase 不要 (buyào; lit. "(I) do not want") may also be used for the interjection "no". (The infamous pirated Chinese version of Star Wars Episode III dubbed Darth Vader's cry of "No!" as "buyào!", which in the English-language subtitles was retranslated as "do not want". This error became an internet meme.)[39]

Japanese also lacks words for yes and no. The words "はい" (hai) and "いいえ" (iie) are mistaken by English speakers for equivalents to yes and no, but they actually signify agreement or disagreement with the proposition put by the question: "That's correct." or "That's incorrect."[34][40] For example: If asked, "行かないのですか" ("ikanai no desu ka" / "Are you not going?"), answering with the affirmative hai would mean "Correct. I am not going"; whereas in English, answering "yes" would be to contradict the negative question. Echo responses are not uncommon in Japanese.

Like the English contraction of Old English yea so into yes, the words for yes and no in other languages originate from a process of devaluation and semantic erosion. The Hungarian strong affirmative persze was originally the Latin phrase per se intelligitur (it stands to reason), for example. German nein similarly is derived from the Old High Germanni ein, which means not a single one. (In Latin, non similarly devolved from noenum, which also means not one.) The French oui was formerly oïl (after which Langue d'oïl is named), which, in turn, came from the Vulgar Latinhoc ille, meaning this one (it is this one).[11]

In Spanish, the words sí (yes) and no (no) are unambiguously classified as adverbs: not only do they serve as answers to questions; they also modify verbs. The affirmative sí can replace the verb after a negation (Yo no tengo carro, pero él sí = I don't own a car, but he does) or intensify it (I don't believe he owns a car. / He does own one! = No creo que él tenga carro. / ¡Sí lo tiene!). The word no is the standard adverb placed next to a verb to negate it (Yo no tengo carro = I don't own a car). Double negation is normal and valid in Spanish, and it is interpreted as reinforcing the negation (No tengo ningún carro = I own no car).

These differences between languages make translation difficult. No two languages are isomorphic, even at the elementary level of words for yes and no. Translation from two-form to three-form systems is something that English-speaking schoolchildren learning French or German soon encounter. But the mapping is not even as simple as converting two forms into three. There are many idioms, such as reduplication (in French, German, and Italian) of affirmatives for emphasis (the German ja ja ja).

Furthermore, the mappings are one-to-many in both directions. The German ja has no fewer than 13 English equivalents that vary according to context and usage (yes, yeah, and no when used as an answer; well, all right, so, and now, when used for segmentation; oh, ah, uh, and eh when used an interjection; and do you, will you, and their various inflections when used as a marker for tag questions) for example. Moreover, both ja and doch are frequently used as additional particles for conveying nuanced meaning where, in English, no such particle exists. Straightforward, non-idiomatic, translations from German to English and then back to German can often result in the loss of all of the modal particles such as ja and doch from a text.[41][42][43][44]

Translation from languages that have word systems to those that do not, such as Latin, is similarly problematic. As Calvert says, "Saying yes or no takes a little thought in Latin"[32]

There are many variants of yes and no in English. Two such spoken forms are transcribed into writing as Uh-huh or Mm-hmm ("yes", with a rise in pitch on the second syllable) and Uh-uh or M-mm ("no", with a fall in pitch on the second syllable). Their sounds are a nasal or non-nasal sound interrupted by a voiceless breathy interval for yes, and by a glottal stop for no. These forms are particularly useful for speakers who are unable to articulate the actual words yes and no because they are using their mouths for other tasks, such as eating for example, or because they are gagged.[45]

The word "aye" is a frequent synonym for "yes", particularly in Scotland, Ireland and northern England, although not always officially acknowledged as such. In December 1993, a witness in a Scottish court who had answered "aye" to confirm he was the person summoned was told by the Sheriff that he must answer either "yes" or "no". When his name was read again and he was asked to confirm it, he answered "aye" again, and was imprisoned for 90 minutes for contempt of court. On his release he said "I genuinely thought I was answering him."[46]

Both words are derived from adverbs in Old English. Yes is derived from a compound of an Old English adverb, yea, which means surely, and so, and is thus surely so, while no comes from an Old English adverb that means never.[1]

Bob Morris Jones (1999). The Welsh Answering System. Walter de Gruyter. ISBN978-3-11-016450-3.—Jones' analysis of how to answer questions with "yes" or "no" in the Welsh language, broken down into a typology of echo and non-echo responsives, polarity and truth-value responses, and numbers of forms